1. Field of the Invention
The invention relates generally to animal cages, and specifically to a system for enriching the environment of animals in cages.
2. Description of Related Art
Ventilated cage and rack systems are well known in the art. One such ventilated cage and rack system is disclosed in U.S. Pat. No. 4,989,545, assigned to Lab Products, Inc., in which an open rack system including a plurality of shelves, each formed as an air plenum is provided. A ventilation system is connected to the rack system for ventilating each cage in the rack. It is known to house rats for study in such a ventilated cage and rack system.
In prior art ventilated cage and rack systems, cages of different sizes are used to accommodate rodents of different types. These cage sizes are selected according to Institute Laboratory Animal Resources (ILAR) guidelines which set non-binding minimums for the size and dimension of cages for particular rodents. For example, for mice that weigh more than 25 grams, a cage having a floor dimension of at least 15 square inches per mouse is required. Similarly, rats up to 400 grams in size require a cage having floor dimensions of at least 40 square inches per rat. Similar requirements are mandated for hamsters and guinea pigs by the Animal Welfare Act (AWA).
A drawback of the prior art cages is that a variety of different cage sizes, necessary to support the different rodent types, must be inventoried and managed so that the appropriate cage size is available for a particular study. For example, the standard rat cage used in the art has a 140 square inch footprint providing for housing of up to three rats in each cage. On the other hand, the standard size for a mouse cage has become 75 inches allowing up to five mice of 25 grams each to be housed therein. Rat cages are also taller than mice cages and therefore the wire bar lid holding food and water is higher from the ground in rat cages than mice cages, therefore one cannot readily house mice in the standard rat cage. This problem is exacerbated in large research facilities, for example, the National Institute of Health (NIH), where 20 to 30 different cage sizes have to be coordinated. Furthermore, each different cage size requires that the corresponding rack that supports the particular cage size and corresponding accessories be used. This forces the facility to inventory and manage a variety of different rack sizes as well.
As in any endeavor, real estate is at a premium in a research facility. Research facilities are only so large and can only accommodate a certain amount of racks. Furthermore, racks and cages must be sized to pass through the standard doors to provide sufficient mobility.
The largest cage racks have been for housing rat cages and generally have a length of about 84.42 inches, a depth of about 26.375 inches and a height of about 77.16 inches. These dimensions allow a rack supporting rat cages thereon to pass through a standard door having a height of 6 feet 8 inches and a width of 36 inches. A rack having these dimensions will accommodate up to thirty-six standard rat cages and therefore will house one hundred and eight rats therein. A mouse rack will have a very similar footprint, namely, a rack having a height of about 77.9 inches, a width of about 75.25 inches and a depth of about 30 inches. Such a rack supports one hundred and forty cages, each cage having a substantially 75 square inch footprint. Since each cage accommodates five mice, the rack can accommodate seven hundred mice.
One disadvantage of prior art cage and rack systems is that the density of rat population supported by a single rack is relatively low compared to the density of the mouse population supported by the rack. Accordingly, it is desired to not only provide a cage which reduces the inventory of cages required to accommodate a number of species, but also to provide a cage and rack system which, within the standard size constraints of the rack, increases the density of the rat population per rack without substantially sacrificing the density of other species housed in the rat cage.
Another disadvantage of some cage and rack systems is that, in certain circumstances, water bottles or automatic watering systems, which are used to provide water to the animals within the cages, fail. Such failures may lead to flooding of the animal's cage or may result in the animal becoming hypothermic, or otherwise ill. In addition, if a large amount of water enters the cage, the animal may drown.
Another disadvantage of some cage and rack systems is that the animal resides solely on the cage floor, which leads to a relatively monotonous existence for the animal within the cage. Such a monotonous lifestyle is not beneficial for the animal, nor is it typically beneficial for studies being performed with the animal. As such, a need exists for an improved animal cage system for housing animals.